1. Field of the Present Invention
The present invention relates to a memory technique, and more particularly, to a multilayered magnetic thin film stack and a nonvolatile memory device having the same.
2. Description of the Related Art
A magnetic random access memory (magnetic RAM or MRAM) is a non-volatile solid magnetic memory device that utilizes a giant magnetic resistance effect or tunneling magnetic resistance effect based on □ phenomenon of spin-dependent conductivity peculiar to a nano-magnetic material. Compared to a phase change RAM (PcRAM) or a resistive RAM (ReRAM), the MRAM is recently being spotlighted due to faster speed and excellent durability against repeated accesses.
A spin transfer torque MRAM (STT-MRAM), which is the most actively researched to implement the MRAM device, exhibits high speed operation, excellent power efficiency, and high-density integration, thus being a leading next-generation memory device. The SU-RAM includes a magnetic tunnel junction (MTJ) structure in which one insulation layer is interposed between two magnetic thin-films. In the MTJ structure, compared to in-plane magnetic anisotropy, perpendicular magnetic anisotropy (also referred to as PMA) features low switching-current density for inversion of magnetization and high thermal stability and is advantageous for scaling devices. Furthermore, since out-of-plane magnetization requires a large magnetic field for unmagnetization and is not energetically unfavorable, strong PMA is preferable.
The PMA may be obtained from intrinsic magneto-crystalline anisotropy of one or more magnetic layers or anisotropy based on interfacial effect (or, interfacial anisotropy) between layers. Generally, if the PMA is based on intrinsic magneto-crystalline anisotropy, high writing current is required, and high fabricating temperature equal to or above 500° C. is required for obtaining crystallinity of the magnetic thin-film. However, PMA based on the interfacial effect may be obtained via a multilayered thin-film stack which can be formed in a general sputtering operation, and may be fabricated at a relatively low temperature below or equal to 300° C., and thus perpendicular magnetization based on the interfacial effect is generally preferable.
However, the perpendicular magnetization using interfacial anisotropy is vulnerable in terms of thermal stability due to perpendicular magnetization property which can be deteriorated in post fabrication process accompanied with thermal budget. The vulnerability directly affects reliability of data storage property and data retention property, and thus solving the low thermal stability of the interfacial anisotropy is demanded.